Rotor blades for helicopters are well known. Rotor blades are also used in vertical and short take off and landing (VSTOL) aircraft. In particular, rotor blades are utilized on VSTOL aircraft in which the rotor blade pivots in relation to the aircraft such that it may provide vertical lift or be rotated to provide horizontal thrust. Typically, rotor blades are long and extend beyond the fuselage of the aircraft. It is thus advantageous to be able to provide a blade which can be folded during shipment or storage so that the blade occupies less space without the need for removal of the blade or blades from the aircraft. Also, recently fiber composite blades have achieved widespread use and have many advantages over metal rotor blades. However, composite blades present unique problems in fabrication and design in order to make a blade which is useful in a folding blade system.
Use of composite materials in rotary blades is attractive because they have unique properties and the structure of composites as well the laminates made from the composites can be tailored to meet specific performance requirements. Composites are based on the controlled distribution of reinforcement material, which may be of one or more materials, in a continuous phase of a matrix material. The composite sheet is formed by arranging the reinforcement material in a desired orientation and covering the reinforcement with the matrix system. These are then typically rolled or otherwise handled to spread the reinforcement evenly and to produce uniform thickness for a sheet. This creates an impregnated system which is partially cured to fix the geometry of the sheet while allowing enough shaped relaxation (drape) and adherence (tack) to permit complex shapes to be built up from the composite sheets thus formed. Prior to cure these composite sheets are referred to as prepreg sheets. In preparation of a laminate part, sheets of composite material are arranged in the desired orientation. In a typical fabrication of complex part the multiple sheets of prepreg material are assembled in the desired orientation. This process is called layup. After layup, the structure formed is cured which bonds the sheets of composite together to form the finished laminated part.
The present invention provides for the construction of a rotor blade which is suitable for producing a composite rotor blade having a design especially suited for folding of the blades to permit for storage without removal of the blade from the aircraft.